Existing mental ray global illumination techniques typically depend on interpolation solutions to trade final quality, and use simplified scene specification for performance, like idealized light sources. Unlike these solutions, the iray rendering mode is based on deterministic and consistent algorithms that converge without introducing persistent approximation artifacts. These algorithms also allow for extreme scalability on parallel computing platforms. On machines equipped with GPU hardware which can be used for general purpose computing, like graphics processors supporting CUDA, this rendering mode is able to achieve interactive frame rates with quick progressive refinement to the desired image quality. This mode enables mental ray to produce images that include the most anticipated but typically expensive real-world effects, including (among others):
In order to achieve this level of realism the scene description - comprising geometry, materials, light sources, and camera model - is interpreted in a manner reflecting physically plausible representations, instead of using traditional shading tricks with approximate models. The rendering process is fully based on BSDF materials and EDF (emission distribution function) light sources, both of which can be coupled with texturing and controlled through intuitive parameters. Existing traditional material descriptions implemented in shaders and established idealized light source types are handled automatically, by emulating them with realistic representations which produce near identical visual results. Programmable shaders implementing illumination algorithms are not required to produce photo-real results.
The iray rendering mode is enabled with a global switch using a scene option or on the command line of standalone mental ray. Since iray is computing images always in progressive rendering mode, it is controlled by relevant options for progressive rendering, like the automatic stop criteria. Part of the environment light pre-computation is performed in regular mental ray, therefore few related environment lighting options apply to iray as well. All the other rendering options for regular mental ray will be ignored silently.
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